Brown the sausage: In a large pot, heat olive oil over medium heat. Add the sausage and cook, breaking it into crumbles, until browned. Remove excess fat if needed.
Sauté the aromatics: Add onion, garlic, and red pepper flakes (if using) to the pot. Cook until softened, about 3-4 minutes.
Build the broth: Stir in tomato paste, crushed tomatoes, broth, Italian seasoning, basil, salt, and pepper. Bring to a gentle boil.
Cook the noodles: Add broken lasagna noodles to the pot. Simmer for 12-15 minutes, stirring occasionally, until noodles are tender.
Cheese swirl: While soup simmers, mix ricotta, mozzarella, and Parmesan in a small bowl.
Serve it up: Ladle soup into bowls. Add a generous spoonful of the cheese mixture on top of each serving. Garnish with fresh basil or parsley.